The development of the lower uterine segment

Association between lower uterine wall thickness measured at 18-22 weeks of gestation and risk of Preterm Birth: a prospective cohort study

Background

Preterm labour prediction has been relied on history of previous preterm birth and cervical length of current pregnancy. However, universal cervical length measurement has some limitation. We aim to find a surrogate marker of cervical length to close the gap in preterm prevention program and lower uterine wall thickness seems promising. We generate the nomogram of lower uterine wall thickness during 18–22 weeks of gestation and evaluate the accuracy of LUW thickness as a predictor of preterm delivery before 37 weeks.

Methods

This prospective cohort study included 524 Thai singleton pregnant women at 18–22 weeks of gestation between November 2016 and October 2017. After signing informed consent, transabdominal ultrasonography was performed to examine fetal anatomical structures and to measure LUW thickness. The results were blinded to the caregivers. The outcomes of all pregnancies were followed. The LUW thickness at 10th percentiles was established and was correlated with the outcomes of pregnancy. The performance of LUW thickness at 10th percentile as a predictor of preterm delivery was calculated. The intra-observer and inter-observer reliability of measurement were assessed by intraclass correlation coefficient and Bland-Altman plot.

Results

Of the 524 pregnant women, 64 (12.2%) delivered before 37 weeks of gestation. The reference value of lower uterine wall thickness at 18–22 weeks was established. Mean and 10th percentile of LUW thickness were 6.2 and 4.5 mm respectively. The inter-observer and intra-observer variation of measurement were small (intraclass correlation coefficient = 0.926 and 0.989 respectively). Using LUW thickness at less than 4.5 mm as a predictor of preterm delivery, we found a 2.37 folds increased risk of preterm delivery after adjustment of other factors (p = 0.037). Sensitivity, specificity, positive predictive value and negative predictive value were 14% (95% CI: 6.64–25.02), 92.8% (95% CI: 90.06–95.12), 22.5% (95% CI: 12.66–36.76) and 88% (95% CI: 86.92–89.08) respectively.

Conclusions

The measurement of LUW thickness by transabdominal ultrasonography is feasible and reproducible. The risk of delivery before 37 weeks of gestation is increased significantly if the LUW thickness at 18–22 weeks is less than 4.5 mm.

Trial registration

The study protocol was approved by institutional ethical committee (COA No. Si 657/2016).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-022-04902-w.

The classification of placenta praevia – time for a change?

The techniques employed in the diagnosis of placenta praevia have altered radically since Guillemeau first described the condition in 1685, stating that ‘The surgeon must consider if it is the child or if it is the after-birth who presents first’. However, his description went unnoted, for Giffart in narrating a case of haemorrhage wrote in 1730: ‘I cannot receive as absolutely true the opinion of those authors, who say that the placenta is always attached to the fundus uteri, for in this case, as in many others, I have every reason to believe that it adhered on the internal orifice, or very near to it; and that, in dilating, the latter occasioned the separation of the after-birth, and as a consequence the haemorrhage.’

Mapping of zones of altered morphology and chorionic connective tissue cellular phenotype in human fetal membranes (amniochorion and decidua) overlying the lower uterine pole and cervix before labor at term

OBJECTIVE

The purpose of this study was to determine the location, frequency, and extent of altered fetal membrane morphology before term labor and its relation to myofibroblast activation in their connective tissue layers.

STUDY DESIGN

Fetal membranes that were obtained from 10 women who underwent prelabor cesarean delivery at 38 to 39 weeks of gestation underwent biopsy examination with respect to the internal os of the cervix. The thickness of their constituent layers was measured, and the numbers of alpha-smooth muscle actin immunoreactive cells (ie, marker of myofibroblast activation) within the reticular layer were counted.

RESULTS

A region that measured 119+/-21cm(2), that exhibited altered morphology of the fetal membranes from the lower uterine pole, and that was characterized by increased connective tissue thickness and decreased thickness of the cellular layers was demonstrated in all patients. In 8 of 10 patients, this region was centered on the location of the Babcock tissue forceps. Within this region was an area of fetal membranes that exhibited alpha-smooth muscle actin immunoreactivity in the cells of the reticular layer and whose number correlated with parameters of altered morphology.

CONCLUSION

All patients before labor at term possess an area of fetal membranes that are located in the lower uterine pole that exhibit altered morphology that is associated with myofibroblastic activation in the chorionic connective tissue.

US of abnormal uterine bleeding

Any significant deviation from a woman's established menstrual pattern may be considered abnormal uterine bleeding, and several factors direct evaluation of a patient with such bleeding. Premenopausal disorders that are well evaluated with ultrasound (US) include endometriosis, adenomyosis, and leiomyomas. A positive pregnancy test in a woman of childbearing age prompts a search for an intrauterine pregnancy. Possible complications that may contribute to bleeding include ectopic pregnancy; placental factors including position, trauma, and infection; gestational trophoblastic disease; preterm labor; and postpartum complications. Atrophic changes, hormonal status, and carcinoma are considerations in the postmenopausal patient with abnormal uterine bleeding. Foreign bodies, trauma, infection, polyps, and iatrogenic causes can be observed in all groups. Differential diagnoses for abnormal uterine bleeding in premenopausal, pregnant, and postmenopausal patients are well evaluated with US, and US techniques have greatly facilitated evaluation of pelvic disease. Urgent and emergent conditions such as ectopic pregnancy, placenta previa, and preterm labor are readily identifiable.

Diagnosis of low-lying placenta: can migration in the third trimester predict outcome?

OBJECTIVES

To investigate the relationship between the rate of migration of a low-lying placenta during the third trimester and the eventual route of delivery.

METHODS

All patients with a placenta lying within 3 cm of the internal cervical os or overlapping it on transvaginal ultrasound at > or = 26 weeks' gestation were included in the study. The exact distance between the center of the internal cervical os and the leading edge of the placenta was measured by transvaginal sonography, repeated at approximately 4-week intervals until delivery.

RESULTS

The mean rates of migration in patients who had (n = 7) and who did not have (n = 29) Cesarean section for placenta previa were +0.3 mm/week and +5.4 mm/week, respectively (P < 0.0001). When the placental edge was initially > 20 mm from the internal os, migration occurred in all cases and no Cesarean section for placenta previa was performed. For those between -20 mm and +20 mm, sufficient migration to avoid Cesarean section occurred in 88.5% of cases. Beyond a 20 mm overlap, significant placental migration did not occur and all patients required Cesarean section.

CONCLUSION

Placental migration may occur progressively throughout the third trimester. The initial position of the placental edge and the subsequent rate of migration can be used to predict the eventual route of delivery.

The role of transvaginal sonography in the diagnosis of placenta praevia

Transvaginal sonography was performed in 70 patients diagnosed to have placenta praevia by transabdominal sonography. The diagnosis was confirmed either by digital examination in theatre at term or operative finding at delivery. Forty-nine cases (70%) were correctly diagnosed to have placenta praevia by both modes of sonography. Transvaginal sonography ruled out placenta praevia in 12 cases (17%) thought to be placenta praevia by transabdominal ultrasound. Both transabdominal and transvaginal sonography demonstrated 'placental migration' in 4 cases (6%) which were no longer praevia at delivery. Five patients (7%) were erroneously believed to have placenta praevia by both sonographic techniques. Overall, the diagnostic accuracy of transvaginal sonography was 92.8% compared with 75.7% for transabdominal sonography. None of the subjects experienced any exacerbation of bleeding or other complications. The results suggest that transvaginal sonographic localization of the placenta is safe and superior to the transabdominal route.

Placenta praevia--a review with emphasis on the role of ultrasound

Considerable confusion exists in the literature as a result of the wide range of classification systems for placenta praevia (PP) and low-lying placenta. The discrepancy between frequency of low-lying placentas in the second trimester and PP at term reflects to a certain extent the lack of understanding of the anatomy and physiology of the pregnant uterus. It seems that 'placental conversion' is a real phenomenon and is probably due to the differential growth rates of the placenta and uterus. Maternal bladder overdistension and myometrial contractions account for only a small part of the discrepancy. Diagnostic ultrasound obviously has an important role in placental localization. The role of Magnetic Resonance Imaging remains to be determined. The management of patients with low-lying placenta diagnosed in the second trimester, and the frequency of repeat scans is determined largely by the management protocol of the attending obstetrician.

Low vertical uterine incision in caesarean section

Eleven of the 3,420 Caesarean sections performed in Westmead Hospital, Sydney during a 6-year period from 1979 to 1985 were by a low vertical uterine incision. All the others were the standard transverse lower segment operation except for 1 which was a postmortem classical Caesarean section. There are indications when the preferred lower segment Caesarean section with a transverse incision should be avoided in the interest of the mother and baby. A low vertical incision has more advantages and less dangers than a classical fundal incision. It is prudent to defer the decision regarding the type of incision until the uterus is inspected intraoperatively. If access to the lower uterine segment is limited by prematurity, an obstructing lesion, a transverse lie, or if the presenting part is high and difficulty in delivering the baby is anticipated, a low vertical incision should be considered.

Classical caesarean section in preterm deliveries

A series of 14 classical Caesarean sections is reported, and the place of operation in certain preterm deliveries is discussed.

The theory, feasibility and accuracy of an ultrasonic method of estimating fetal weight

We present the theory, method, feasibility and accuracy of estimating fetal weight by measuring the fetal volume using compound ultrasonic scanning. The two parameters had a very high coefficient of correlation (0-9794), and the standard error in one series of 20 patients was only +/- 106 g. The correlation coefficient achieved by one of us who was new to ultrasound techniques was 0-82, which compared favourably with correlations between fetal weight and biparietal diameter measurements (r = 0-26). A discussion as to the correction factors required to allow for the unknown value of the velocity of ultrasound in fetal tissues, the clinical use of this method, and the possible means by which the accuracy of estimating fetal weight may be further improved is included.